The measured -4°C should be correct.Reason: The reference voltage for the AD converter has been defined by yourself with 1100mV.According to the datasheet of the sensor, the voltage which will be provided by the sensor at +125°C will be 1205mV (1205mV > VRef).The maximum voltage which will be converted by the ADC is 1100mV. In case you will set 1205mV on the ADC pin, I would expect that there will be an overflow in the µC. Due to that the reference voltage has not been adapted to the max sensor voltage, you will get a lower temparetaure as expected.Also the behaviour U=f(T) of the sensor is not linear according the reference points you mentioned from the datasheet.

The measured -4°C should be correct.Reason: The reference voltage for the AD converter has been defined by yourself with 1100mV.According to the datasheet of the sensor, the voltage which will be provided by the sensor at +125°C will be 1205mV (1205mV > VRef).The maximum voltage which will be converted by the ADC is 1100mV. In case you will set 1205mV on the ADC pin, I would expect that there will be an overflow in the µC. Due to that the reference voltage has not been adapted to the max sensor voltage, you will get a lower temparetaure as expected.Also the behaviour U=f(T) of the sensor is not linear according the reference points you mentioned from the datasheet.

I agree with you, I am using Vref = 1100mV but the real value is 1088 (assuming my multimeter is correct).

But, to explain the real problem, imagine this:

Forget the LM60.

I use my stable power supply, and adjust the ouput voltage with the help of my multimeter to 424mV.

Then I apply that voltage to the analog input.

The real voltage is 424mV. The ADC has error (because of Vref) and measures 400mV.

For a 10-bit ADC with an 1100 mV reference, the most you can measure without saturating the ADC would be (1100 mV - 1100/1024 mV) = 1098.9 mV.In other words, a reading of 1023 from your ADC equals (1023 * 1100/1024 mV) equals 1098.9 mV. Remember, 10 bits can only represent a value as large as b1111111111 or decimal 1023.